The invention relates to rifle receivers and, more particularly, to improvements in pivot axis pin fixtures therein. Additionally, the invention relates to a threaded assembly pin and, more particularly, to replacement of conventional roll pins for assembly of not only the bolt catch mechanism of an AR-15 firearm but also the forward assist mechanism.
The improvements of invention were inspired in particular with improving the design(s) of AR-15 lower housings, and like style of firearms. Nowadays, the features of AR-15 lower housings are typically machined from aluminum castings. After the machining operations, certain accessories are mounted to the aluminum lower housing as a subsequent assembly operation.
For example, various pivoting parts are mounted to the aluminum lower housing by means of pivot axis pins typically produced from steel, and then mounted in bores therefor bored into the receiver. Such pivoting parts include without limitation the hammer and trigger (which are mounted on laterally extending pins), the forward assist mechanism, or else bolt stop release mechanism and the like (which are typically mounted on longitudinally extending pins).
The hammer and trigger for an AR-15 lower housing are typically mounted on pins which are not intended to rotate. Hence the pins are intended to be fixtures. The hammer and trigger are mounted to pivot on these fixed pins.
The pins are preferably mounted as follows. That is, the pins typically have smooth cylindrical walls. The pins are mounted in the manner of being ‘simply supported’ at their opposite ends in spaced bores therefor in the spaced left and right sidewalls of the lower housing (or spaced port and starboard sidewalls thereof). This way, the pins span across a hollow interior of the lower housing in which is laterally confined the hammer and trigger for each respective pin. Preferably each pin is slid through one of the bores therefor in one sidewall of the lower housing (preferably a bore that provides a close fit). Then the pin is slid through a counterpart bore therefor in the respective hammer or trigger. Finally the pin is preferably press fitted into the opposite bore therefor in the spaced sidewall of the lower housing, wherein this bore is slightly undersized to force an interference fit.
In this manner, the pins are intended to be fixtures for the hammer and trigger to pivot thereon. However, after many cycles of firing and re-loading, the pins are vibrated to such an extent that the pins start to work loose in their close fits and/or press fits. The pins might also seize in the mounting bores therefor in the hammer and/or trigger.
That is, the hammer and trigger as well as the pins therefor are typically steel parts (eg., hard materials) which tend to seize (eg., the hammer or trigger with its respective pin) if there is any problem at the cylindrical interface therebetween. In other words, if there are any problems between the hammer and trigger and each one's respective pin, relative pivoting will likely be eliminated due to seizure. Such sources of problems leading to seizure include any of wear, distortion, corrosion, erosion, and so on.
The housing, typically being made of a softer material, typically suffers. If the pins were originally tightly held by the housing due to a press fit, but subsequently seize with the hammer of trigger, the pins will thereafter spin in their press fit bores in the housing. Given enough use, the features which mount the pins (or are mounted on the pins) start to distort. The pins may start to rotate during the actuation of the hammer and/or trigger.
The pins and the mounting holes therefor in both sidewalls of the lower housing as well as in the hammer and trigger are designed in accordance with tight tolerances not just for optimal performance but also to avoid ruination to unacceptable performance.
But as mentioned previously, the pins are made of steel while the lower housing is typically made of aluminum. This unfortunately makes the lower housing more susceptible to any damage when things begin to function abnormally. What normally happens is that the pins begin to rotate, slightly at first. This causes the bores to become oversized and/or egg shaped.
As the mounting bores are compromised by enlargement, the lower housing is unable to maintain its positioning tolerance as required by engineering specification therefor. The engineering specification for the function of the hammer and trigger pins is such that the pins are meant to be stable while the hammer and trigger pivot about the pins.
Once this initial deformation occurs, there is an exponential amount of damage caused after each use. In time, dramatic steps need to be taken to amend the damage, and sometimes it renders a lower housing damaged beyond repair.
To turn attention now more particularly to the bolt catch feature of an AR-15 firearm, the conventional way to assemble the bolt catch mechanism has been to use roll pins. That is, the forward assist mechanism would be positioned and locked into place using a roll pin. The roll pin would be typically positioned and driven in place by use of a punch. To disassemble the pin, such a roll pin would have to be driven back out with use of the punch again.
Such hammering back and forth is difficult for a majority of individuals to perform in such delicate circumstances. Moreover, such hammering risks increased chances of damaging the housing if the pin is driven in incorrectly (and also if the punch slips).
The foregoing problems are likely and exacerbated by the small-scale working room afforded to a user attempting to drift punch such rolls pins.
Here is why. The pivot pin for the forward assist mechanism is typically ‘simply supported’ across gap between a pair of spaced bosses (eg., raised protrusions). These bosses are typically raised on the outer sidewall of the lower housing, just forward of the trigger, and on the side opposite of the user's trigger-pulling hand. Each boss (eg., raised protrusion) will need to have a through hole for the roll pin. That is because, the through hole in one boss allows for insertion of the pin. The through hole in the opposite boss either allows for the roll pin to be pushed through until the pin falls out, or else insertion of the punch to push the pin out in reverse (eg., back out the hole it was inserted through).
There are many many problems with the foregoing. These bosses are just slight protrusions off the sidewall of the housing. The roll pin is intended to be disposed on a pivot axis which just barely clears the plane of the housing sidewall. Therefore, the main problems are with the punch tool. With allegorical reference to children stories, the punch tool can be likened to Gulliver in a Lilliputian work-environment. If the punch tool has a radius larger than the gap between the pivot axis of the roll pin and the housing sidewall, the punch tool cannot drive the roll pin on axis. The punch tool can only do so at an oblique angle. If, to solve that problem, the punch tool is made especially slender (but long), then the chances of driving the pin straight are only likely to the skilled, the lucky, or just the skilled and lucky. And then there is the clearance of features on the sidewall of the of the housing to give a flight path for the punch from both sides of the housings, or, from the side of just one housing but clearance for the pin to push out from the opposite side of the opposite housing.
The problems with the roll pin insertion and removal for the forward assist mechanism according to the prior art are rife. What are needed are solutions over the shortcomings of the prior art.
To be brief about the forward assist mechanism, it enables the AR-15 user to manually drive the bolt carrier forward when the carrier becomes jammed. There is a socket or cavity in the rifle receiver lower housing for the forward assist mechanism to be inserted into. The conventional way for retaining the forward assist mechanism in its socket has been to use a roll pin. The forward assist mechanism could likewise benefit by the replacement of roll pins with a threaded assembly pin.
A number of additional features and objects will be apparent in connection with the following discussion of the preferred embodiments and examples with reference to the drawings.